My 400/4 starts on four, goes very nicely but when it warms up it begins to misfire, first on one pair of cylinders (my guess,) followed very shortly afterwards by the other two conking out and silence. A few minutes later it runs again but not for long.
Because it doesn't run reliably, I haven't ridden it home as was the plan (Le Mans to Cherbourg then on the boat to Poole where I live.)
If it were one pair, you would say condenser. If it is both pairs though, it seems a long shot that both have failed. Because they fail in turn, it rules out the ignition and kill switches and running with the tank cap open has ruled out fuel starvation.
If somebody told me that the exhaust valve clearances were too tight, It would be believeable although I would expect to lose cylinders one at a time so it seems unlikely to be that. The PO changed coils and probably condensers. I shall be taking out new condensers to fit and try, a new battery, a good multimeter and half a century's electronics know how. I plan to check the earthing of the points plate, the field coil regulator, I have a new rectifier if needed and obviously the stator and field coil resistances and their ground isolation. When it is running, it is clearly well carburated with no flat spots and access to the upper reaches of the tacho as well as that addictive howl so there isn't anything apparently wrong with the fuelling. Testing the plug caps to see if they are resistive and checking the plugs to ensure that they aren't is on the list but this one looks like it may be tricky to isolate so any ideas would be welcome if you have seen this bug before.
